1. Field of the Invention
This invention relates to a process for preparing fluoroethylenes and chlorofluoroethylenes by hydrogenolysis of chlorofluoroethanes, comprising also the compounds which contain, besides chlorine and fluorine, one or more hydrogen atoms.
2. The Prior Art
Fluoroethylenes and chlorofluoroethylenes are halogenated olefins well known in literature and they are advantageously utilized as intermediates in the preparation of fluoroplastomers, fluoroelastomers and as comonomers in the preparation of fluorinated copolymers.
Fluorine-containing olefins are generally prepared by dehydrohalogenation or dehalogenation of the corresponding haloalkanes in the liquid phase, according to well known modalities. For example, 1-chloro-1,2-difluoroethylene and 1,2-dichloro-dichloroethylene are prepared by reduction, with zinc in an alcohol solution, of 1,2-difluoro-1,1,2-trichloroethane and 1,2-difluoro-tetrachloroethane, respectively (J. Chem. Soc. London 1957, pages 2800-06). The high addition of zinc necessary to the reaction and its difficult removal render these processes little attractive from an industrial viewpoint.
The preparation of 1,2-difluoroethylene using 1,2-difluoro-tetrachloroethane as a starting material is described in literature. Said reaction occurs in two steps, the former comprising the obtaining of 1,2-difluoro-1,2-dichloroethane through reduction by means of LiAlH.sub.4 or through UV-radiations in the presence of 2-propanol, while the latter consists in the dehalogenation of the abovesaid intermediate in the presence of Mg. (Collection Czechloslov. Chem. Commun. Vol. 39, (1974) pages 2801-07).